Non-toxic, environmentally benign fire extinguishants

ABSTRACT

Flooding fire extinguishing agents which are non-toxic and environmentally safe in both natural form and in degraded form which may occur as a result of exposure to fire are disclosed. The flooding fire extinguishing agents are rich in low boiling unsaturated chlorofluorocarbon compounds and have low liquid viscosities.

FIELD OF THE INVENTION

This invention pertains to fire extinguishing agents which are non-toxicand environmentally safe in both natural form and in degraded formswhich may occur as a result of exposure to fire.

DESCRIPTION OF THE PRIOR ART

U.S. Pat. No. 4,954,271, issued Sep. 4, 1990, Raymond W. Green,discloses and protects environmentally amicable fire extinguishingagents comprising in combination: (a) more than 50% by weight of afluorochlorocarbon selected from the group consisting of:1,1-dichloro-2,2,2-trifluoroethane, and 1,2-dichloro-2,2-difluoroethane;(b) less than 48% by weight of a fluorocarbon selected from the groupconsisting of: chlorodifluoromethane,1-chloro-1,2,2,2-tetrafluoroethane, pentafluoroethane,1,2,2,2-tetrafluoroethane; and (c) a substance selected from the groupconsisting of terpenes: citral, citronellal, citronellol, limonene,dipentene, menthol, terpinene, terpinolene, sylvestrene, sabinene,methadiene, zingiberene, ocimene, myrcene, α-pinene, β-pinene,turpentine, camphor, phytol, vitamin A, abietic acid, squalene,lanosterol, saponin, oleanolic acid, lycopene, β-carotene, lutein,α-terpineol, and p-cymeme; and unsaturated oils; oleic acid, linoleicacid, linolenic acid, eleosearic acid, lincanic acid, ricinoleic acid,palmitoleic acid, petroselenic acid, vaccenic acid, and erucic acid, inthe range of from 2 to 10% by weight.

U.S. Pat. No. 4,826,610, issued May 2, 1989, Derek A. Thacker, disclosesa firefighting composition comprising one or more of Halons 11, 12, 113and 114 together with 1% to 14% by weight of an extinguishant baseincluding a sesquiterpene and one or more essential oils. Solvents anddispersing agents may also be provided. This composition is suited forstream type firefighting situations. The formulation is not particularlyozone friendly.

G.B. Patent No. 1,603,867, Derek A. Thacker, Dec. 2, 1981, discloses afire extinguisher formulation comprising trichlorofluoromethane(Halocarbon Number 11) and an additive comprised of a mono-terpene. Theadditive can include an essential oil such as citrus oil or pinene.Dichlorofluoromethane (Halocarbon Number 12) can be included in theformulation.

SUMMARY OF THE INVENTION

A fire extinguishing mixture of the following compounds:

(a) 90 to 99.9% wt. of one or more halocarbons of the formula:

    C.sub.W H.sub.X Cl.sub.Y F.sub.Z

wherein W is 1, 2, 3 or 4, X is any one of 0 to 9, Y is any one of 0 to9 and Z is any one of 1 to 10, provided when W is 1, X is 0 to 2, Y is 0to 2, and Z is 1 to 3, the total to add up to 4; when W is 2, X is 0 to4, Y is 1 to 5, and Z is 1 to 5, the total to add up to 6; when W is 3,X is 0 to 6, Y is 0 to 7, and Z is 1 to 8, the total to add up to 8; andwhen W is 4, X is 0 to 8, Y is 0 to 9, and Z is 1 to 10, the total toadd up to 10; and

(b) 0.1 to 10% wt. of one or more detoxifying substances selected fromthe group consisting of:

    ______________________________________                                        citral       citronellal   citronellol                                        limonene     dipentene     menthol                                            terpinene    terpinolene   sylvestrene                                        sabinene     menthadiene   zingiberene                                        ocimene      myrcene       alpha-pinene                                       beta-pinene  turpentine    camphor                                            phytol       vitamin A     abietic acid                                       squalene     lanosterol    saponin                                            oleanolic acid                                                                             lycopene      beta-carotene                                      lutein       alpha-terpineol                                                                             para-cymene                                        oleic acid   linoleic acid linolenic acid                                     eleostearic acid                                                                           lincanic acid ricinoleic acid                                    palmitoleic acid                                                                           petroselenic acid                                                                           vaccenic acid                                      erucic acid  ethene        propene                                            butene       isopropene    pentene                                            isopentene   trimethylethene                                                                             tetramethylethene                                  butadiene    2-methylbutadiene                                                                           pentadiene                                         isobutylene                                                                   ______________________________________                                    

the mixture having a boiling point of about -85° C. to about 200° C., amolecular weight in the range of 70 to 400, and a vapour pressure ofabout MPa 0.1 to about 5.

A fire fighting mixture of the formula:

(a) 90% to 99.9% wt. of a chlorofluorocarbon or fluorocarbon selectedfrom the group consisting of:

    ______________________________________                                        hydrochlorofluorocarbon.13 -                                                                    chlorotrifluoromethane                                      hydrochlorofluorocarbon.21 -                                                                    dichlorofluoromethane                                       hydrochlorofluorocarbon.22 -                                                                    chlorodifluoromethane                                       hydrochlorofluorocarbon.31 -                                                                    chlorofluoromethane                                         hydrochlorofluorocarbon.121 -                                                                   1,1,2,2-tetrachloro-                                                          1-fluoroethane                                              hydrochlorofluorocarbon.122 -                                                                   1,1,2-trichloro-2,2-                                                          difluoroethane                                              hydrochlorofluorocarbon.123 -                                                                   2,2-dichloro-1,1,1-                                                           trifluoroethane                                             .sup.             1,2-dichloro-1,1,2-                                                           trifluoroethane                                             hydrochlorofluorocarbon.124 -                                                                   2-chloro-1,1,1,2-                                                             tetrafluoroethane                                           .sup.             1-chloro-1,1,2,2-                                                             tetrafluoroethane                                           hydrochlorofluorocarbon 125 -                                                                   pentafluoroethane                                           hydrochlorofluorocarbon.131 -                                                 hydrochlorofluorocarbon.132 -                                                                   1,2-dichloro-1,1-                                                             difluoroethane                                              hydrochlorofluorocarbon.133 -                                                                   2-chloro-1,1,1-                                                               trifluorethane                                              hydrochlorofluorocarbon.134a -                                                                  1,1,1,2-                                                                      tetrafluoroethane                                           hydrochlorofluorocarbon.141 -                                                                   1,2-dichloro-1-                                                               fluoroethane                                                .sup.             1,1-dichloro-1-                                                               fluoroethane                                                                  hexafluoropropane                                           hydrochlorofluorocarbon.142 -                                                                   1-chloro-1,1-                                                                 difluoroethane                                              hydrochlorofluorocarbon.221 -                                                                   2-fluorohexachloropropane                                   hydrochlorofluorocarbon.222 -                                                                   1,1-difluoro-1,2,2,3,                                                         3-pentachloropropane                                        hydrochlorofluorocarbon.223 -                                                 hydrochlorofluorocarbon.224 -                                                 hydrochlorofluorocarbon.225 -                                                                   3,3-dichloro-1,1,1,2,                                                         2-pentafluoropropane                                        .sup.             1,3-dichloro-1,1,2,2,                                                         3-pentafluoropropane                                        hydrochlorofluorocarbon.226 -                                                 hydrochlorofluorocarbon.231 -                                                 hydrochlorofluorocarbon.232 -                                                 hydrochlorofluorocarbon.233 -                                                 hydrochlorofluorocarbon.234 -                                                 hydrochlorofluorocarbon.235 -                                                 hydrochlorofluorocarbon.241 -                                                 hydrochlorofluorocarbon.242 -                                                                   1,1,1-trichloro-2,2-                                                          difluoropropane                                             hydrochlorofluorocarbon.243 -                                                 hydrochlorofluorocarbon.244 -                                                 hydrochlorofluorocarbon.251 -                                                 hydrochlorofluorocarbon.252 -                                                 hydrochlorofluorocarbon.253 -                                                                   2-chloro-1,1,1-                                                               trifluoropropane                                            hydrochlorofluorocarbon.261 -                                                                   1,2-dichloro-2-                                                               fluoropropane                                               hydrochlorofluorocarbon.262 -                                                 hydrochlorofluorocarbon.271 -                                                 ______________________________________                                    

(b) 0 to 10% of one or more detoxifying substance selected from thegroup consisting of:

    ______________________________________                                        citral       citronellal   citronellol                                        limonene     dipentene     menthol                                            terpinene    terpinolene   sylvestrene                                        sabinene     menthadiene   zingiberene                                        ocimene      myrcene       alpha-pinene                                       beta-pinene  turpentine    camphor                                            phytol       vitamin A     abietic acid                                       squalene     lanosterol    saponin                                            oleanolic acid                                                                             lycopene      beta-carotene                                      lutein       alpha-terpineol                                                                             para-cymene                                        oleic acid   linoleic acid linolenic acid                                     eleostearic acid                                                                           lincanic acid ricinoleic acid                                    palmitoleic acid                                                                           petroselenic acid                                                                           vaccenic acid                                      erucic acid  ethene        propene                                            butene       isopropene    pentene                                            isopentene   trimethylethene                                                                             tetramethylethene                                  butadiene    2-methylbutadiene                                                                           pentadiene                                         isobutylene                                                                   ______________________________________                                    

A fire extinguishing mixture for use in a flooding technique in anenclosed volume comprising:

(a) more than 50 percent by weight of a substance selected from thegroup consisting of:

dichlorodifluoromethane,

1,2-dichlorotetrafluoroethane,

chlorodifluoromethane,

1-chloro-1,2,2,2-tetrafluoroethane,

1,1-dichloro-2,2,2-trifluoroethane,

1,2,2,2-tetrafluoroethane,

pentafluroethane;

(b) less than 48 percent by weight of a substance selected from thegroup consisting of:

trichlorofluoromethane,

1,1-dichlorotetrafluoroethane,

1,2-dichloro-2,2-difluoroethane; and

c) between 0.25 and 10 percent by weight of a detoxifying substanceselected from the group consisting of:

    ______________________________________                                        citral       citronellal   citronellol                                        limonene     dipentene     menthol                                            terpinene    terpinolene   sylvestrene                                        sabinene     menthadiene   zingiberene                                        ocimene      myrcene       alpha-pinene                                       beta-pinene  turpentine    camphor                                            phytol       vitamin A     abietic acid                                       squalene     lanosterol    saponin                                            oleanolic acid                                                                             lycopene      beta-carotene                                      lutein       alpha-terpineol                                                                             para-cymene                                        oleic acid   linoleic acid linolenic acid                                     eleostearic acid                                                                           lincanic acid ricinoleic acid                                    palmitoleic acid                                                                           petroselenic acid                                                                           vaccenic acid                                      erucic acid  ethene        propene                                            butene       isopropene    pentene                                            isopentene   trimethylethene                                                                             tetramethylethene                                  butadiene    2-methylbutadiene                                                                           pentadiene                                         isopropenyl-1-methyl-      isobutylene                                        cyclohexene                                                                   ______________________________________                                    

The initial boiling point of the mixture can be between -80° C. and -10°C. The fluid viscosity of the mixture can be below 1.0 centipoise in therange between the initial boiling point of the mixture and 25° C.

A fire extinguishing mixture for use in a flooding technique in anenclosed volume comprising:

(a) at least 50 percent by weight of a substance selected from the groupconsisting of:

chlorodifluoromethane,

dichlorodifluoromethane;

(b) less than 48 percent by weight of a substance selected from thegroup consisting of:

1-chloro-1,2,2,2-tetrafluoroethane,

1,2-dichlorotetrafluoroethane,

trichlorofluoromethane,

1,1-dichloro-2,2,2-trifluoroethane; and

(c) between 2 and 4 percent by weight of a substance selected from thegroup consisting of:

dipentene, and

limonene.

A specific fire extinguishing mixture can consist essentially of about96 percent by weight of chlorodifluoromethane, and about 4 percent byweight of limonene. Another specific fire extinguishing mixture canconsist essentially of about 85 percent by weight ofchlorodifluoromethane, about 11.5 percent by weight of1-chloro-1,2,2,2-tetrafluoroethane, and about 3.5 percent by weight ofdipentene.

A further embodiment of fire extinguishing mixture can consistessentially of about 65 percent by weight of dichlorodifluoromethane,about 15.5 percent by weight of 1,2-dichlorotetrafluoroethane, about15.5 percent by weight of trichlorofluoromethane, and about 4 percent byweight of limonene. A further version of fire extinguishing mixture canconsist essentially of about 65 percent by weight ofdichlorodifluoromethane, about 15.5 percent of1,2-dichlorotetrafluoroethane, about 15.5 percent by weight oftrichlorofluoromethane, and about 4 percent by weight of dipentene.

A variation embodiment of the fire extinguishing mixture can consistessentially of about 75 percent by weight of chlorodifluoromethane,about 11.75 percent by weight of 1,1-dichloro-2,2,2-trifluoroethane,about 9.5 percent by weight of 1-chloro-1,2,2,2-tetrafluoroethane, andabout 3.75 percent by weight of limonene.

An alternative embodiment comprises about 4.75% wt. of2,2-dichloro-1,1,1-trifluoroethane, about 82% wt. ofchlorodifluoromethane, about 9.5% wt. of2-chloro-1,1,1,2-tetrafluoroethane and about 3.75% wt.isopropenyl-1-methyl cyclohexene.

The initial boiling point of the mixture preferably can be between -80°C. and -10° C. The fluid viscosity of the mixture can be below 1.0centipoise between the initial boiling point of the mixture and 25° C.

A fire extinguishing mixture of the formula:

(a) about 1% wt. of 2,2-dichloro-1,1,1-trifluoroethane or1,2-dichloro-1,1,2-trifluoroethane;

(b) about 9.5% wt. of 2-chloro-1,1,1,2-tetrafluoroethane or1-chloro-1,1,2,2-tetrafluoroethane;

(c) about 79.5 to 88.5% wt. of chlorodifluoromethane; and

(d) about 1 to 10% wt. of isobutylene.

A fire extinguishing mixture of the formula:

(a) about 4 to 45% wt. of 2-chloro-1,1,1,2-tetrafluoroethane or1-chloro-1,1,2,2-tetrafluoroethane;

(b) about 50 to 90% wt. of pentafluoroethane; and

(c) about 0 to 10% wt. of isobutylene.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In this disclosure, the word "fire" refers explicitly to standardizedtesting fires as defined by authoritative regulatory bodies havingjurisdiction in the areas of fire control, fire prevention, and firefighting.

We have invented a family of new chlorofluorocarbon and fluorocarbonfire extinguishing agents that cause minimum damage to the ozone layerof the earth. The agents contain no bromofluorocarbons which have beendiscovered to have serious ozone damaging effect. Also, since chlorineis being discovered to be potentially harmful to the ozone layer,chlorine content of the chlorofluorocarbons has been minimized.

A standard regulatory test for evaluating flooding type fireextinguishants uses a test chamber measuring 0.5×3×3 meters containingfive pot fires distributed evenly in the space. The extinguishant to betested is pumped through a pipe system measuring 3 meters. A kilogram ofextinguishant is pumped through the pipe system and the time taken toextinguish the fires is measured.

When a flooding or inerting fire extinguishing technique is to be used,that is, where the extinguishant is released into an enclosed volumecontaining a fire, we have discovered that fires of this type are bestextinguished using mixtures as follows:

(a) more than 50 percent by weight of the following seven compounds,singly or in combination:

dichlorodifluoromethane,

1,2-dichlorotetrafluoroethane,

chlorodifluoromethane,

1-chloro-1,2,2,2-tetrafluoroethane,

1,2,2,2-tetrafluoroethane,

1,1-dichloro-2,2,2-trifluoroethane,

pentafluroethane;

(b) less than 48 percent by weight of the following three compounds,singly or in combination:

trichlorofluoromethane,

1,1-dichlorotetrafluoroethane,

1,2-dichloro-2,2-difluoroethane; and

(c) between 0.25 and 10 percent by weight of any one or more of thefollowing fifty-one alkenes, terpenes and unsaturated oils:

    ______________________________________                                        citral       citronellal   citronellol                                        limonene     dipentene     menthol                                            terpinene    terpinolene   sylvestrene                                        sabinene     menthadiene   zingiberene                                        ocimene      myrcene       alpha-pinene                                       beta-pinene  turpentine    camphor                                            phytol       vitamin A     abietic acid                                       squalene     lanosterol    saponin                                            oleanolic acid                                                                             lycopene      beta-carotene                                      lutein       alpha-terpineol                                                                             para-cymene                                        oleic acid   linoleic acid linolenic acid                                     eleostearic acid                                                                           lincanic acid ricinoleic acid                                    palmitoleic acid                                                                           petroselenic acid                                                                           vaccenic acid                                      erucic acid  ethene        propene                                            butene       isopropene    pentene                                            isopentene   trimethylethene                                                                             tetramethylethene                                  butadiene    2-methylbutadiene                                                                           pentadiene                                         isobutylene                                                                   ______________________________________                                    

The precise choice of agents and compositions will be governed by abalance of cost, factors governing fluid and vapor flow, factorsgoverning fluid and vapor physical characteristics, and theconfiguration of the extinguishant flooding system needed to protect theintended volume(s).

It has been discovered that for extinguishing fires in enclosed volumesby flooding or inerting techniques, it is critical that the fluidviscosity and initial boiling points of the fire extinguishant are low.A number of other criteria are also important. The mixtures we haveinvented that are suitable for flooding or inerting fire extinguishingagents have the following characteristics and attributes:

1. The class of fire flooding mixtures according to the invention mustbe richer in lower boiling compounds, and not exhibit much cohesion. Theflooding class described will rapidly vaporize and flood the intendedvolume to the concentration of extinguishant required to smother orinert the gaseous phase and prevent or extinguish an included fire.

2. The lower boiling points exhibited by this class of floodingmixtures, can permit the list of detoxifying agents to include lowboiling alkenes which cannot be successfully used with streamingextinguishants.

3. The relative quantities of detoxifying alkene, terpene, andunsaturated oil in the flooding mixtures described can be reducedbecause the flooding technique uses a fixed but larger quantity ofextinguishing mixture than is required for streaming type agents.

4. The low boiling fluorochlorocarbons listed in list (a) produce lowerquantities of toxic halogens and hydrogen halides upon decompositionthan do the higher boiling fluorochlorocarbons in list (b). This permitslesser quantities of detoxifying agents to be used.

5. When the detoxifying agents are eliminated completely from the fireextinguishing mixtures, we have found that fire extinguishing is lessefficient than when the detoxifying compounds are included. Also,dangerous levels of toxic halogen and hydrogen halides are produced whenthe extinguishant mixture is decomposed by the heat of the fire.

6. The physical characteristics of a flooding mixture should have aboiling range between -80° C. and -10° C. It should also have a liquidviscosity less than 1.0 centipoise in the temperature range from theinitial boiling point of the mixture to approximately 25° C.

EXAMPLE 1

In one particular test, a test chamber measuring 0.5×3×3 meters andcontaining five standard pot fires was flooded pumping a pipe systemabout 3 meters in total length. The pot fires were inerted in less than10 seconds by using 1 kg of a mixture consisting of 96 percent by weightof chlorodifluoromethane and 4 percent by weight of limonene through thepipe. This mixture had an initial boiling point of -40.5° C. and aliquid viscosity of 0.21 centipoise at 25° C.

EXAMPLE 2

In another evaluation using the same test chamber as in Example 1, thefive pot fires were inerted in less than 10 seconds using 1 kg of amixture consisting of 85 percent by weight of chlorodifluoromethane,11.5 percent by weight of 1-chloro-1,2,2,2-tetrafluoroethane, and 3.5percent by weight of dipentene.

EXAMPLE 3

In a third test using the same test chamber as in Example 1, the fivepot fires were inerted in less than 10 seconds using 1 kg of a mixtureconsisting of 65 percent by weight of chlorodifluoromethane, 15.5percent by weight of 1,2-dichlorotetrafluoroethane, 15.5 percent byweight of trichlorofluoromethane, and 4 percent by weight of limonene.This mixture had an initial boiling point of -27° C. and a fluidviscosity of 0.28 centipoise at 25° C.

EXAMPLE 4

In a fourth application using the same test chamber as in Example 1, thefive pot fires were inerted in less than 10 seconds using 1 kg of amixture consisting of 65 percent by weight of dichlorodifluoromethane,15.5 percent by weight of 1,2-dichlorotetrafluoroethane, 15.5 percent byweight of trichlorofluoromethane and 4 percent by weight of limonene.This mixture exhibited an initial boiling point of -13° C. and aviscosity of 0.36 centipoise at 25° C.

EXAMPLE 5

In a fifth test using the same test chamber as in Example 1, the fivepot fires were inerted in less than 10 seconds using 1 kg of a mixtureconsisting of about 65 percent by weight of dichlorodifluoromethane,about 15.5 percent of 1,2-dichlorotetrafluoroethane, about 15.5 percentby weight of trichlorofluoromethane, and about 4 percent by weight ofdipentene.

EXAMPLE 6

In a sixth evaluation using the same test chamber as in Example 1, thefive pot fires were inerted in less than 10 seconds using 1 kg of amixture consisting of about 75 percent by weight ofchlorodifluoromethane, about 11.75 percent by weight of1,1-dichloro-2,2,2-trifluoroethane, about 9.5 percent by weight of1-chloro-1,2,2,2-tetrafluoroethane, and about 3.75 percent by weight oflimonene.

These examples vividly demonstrate the key role that low fluid viscosityand low boiling point plays in parameterizing the mixtures required toachieve optimum volume of fire extinguishing performance. The goal is toachieve mixtures having an initial boiling point approximating -60° C.and a fluid viscosity approximating 0.15 centipoise at 25° C.

The following ozone benign formulation has been invented to replaceHalon 1301, which is a well known and widely used chlorofluorocarbonflooding extinguishant:

    ______________________________________                                        2,2 dichloro-1,1,1-trifluoroethane -                                                                  4.75%   wt.;                                          chlorodifluoromethane - 82%     wt.;                                          2 chloro 1,1,1,2-tetrafluoroethane -                                                                  9.5%    wt.;                                          isopropenyl-1-methyl cyclohexene -                                                                    3.75%   wt.                                           ______________________________________                                    

The properties of this formulation (called NAF S-III) compared to Halon1301 are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Physical Properties                                                                             Halon 1301 NAF S-III                                        ______________________________________                                        Ozone depletion potential                                                                       10.00      0.044                                            Global warming potential                                                                        .80        .31                                              Lifetime          107 years  7 years                                          Molecular weight  148.95     92.9                                             Boiling point at 1 atm. °C.                                                              -57.75     -38.3                                            Critical temperaturre °C.                                                                67         125                                              Critical pressure (psia)                                                                        67.0       66.5                                             (760 mmHg = 14.7 psia)                                                        Critical density (kg/m.sup.3)                                                                   745        580                                              Density of liquid at 25°                                                                 1.57       1.20                                             (g/ml)                                                                        Specific heat of liquid at                                                                      870        1250                                             25° C. [J/(kg. °C.)]                                            Heat of vaporization at                                                                         118.8      227                                              boiling point (kJ/kg)                                                         viscosity of liquid                                                                             0.159      0.21                                             at 25° C.  centipoise centipoise                                       Acute toxicity (ALC.sub.50                                                                      400-800,000*                                                                             290,000                                          rats: 4 hrs-ppm)                                                              Solubility in water                                                                             0.03       0.0835                                           at 25° C.  weight %   weight %                                         ______________________________________                                         *estimated values                                                        

I claim:
 1. A fire extinguishing mixture comprising:(a) about 1% wt. of2,2-dichloro-1,1,1-trifluoroethane or1,2-dichloro-1,1,2-trifluoroethane; (b) about 9.5% wt. of2-chloro-1,1,1,2-tetrafluoroethane or1-chloro-1,1,2,2-tetrafluoroethane; (c) about 79.5 to 88.5% wt. ofchlorodifluoromethane; and (d) about 1 to 10% wt. of isobutylene, saidfire extinguishing mixture being non-toxic and environmentally benign inboth natural form and degraded form on exposure to fire.
 2. A fireextinguishing mixture comprising about 4.75% wt. of2,2-dichloro-1,1,1-trifluoroethane, about 82% wt. ofchlorodifluoromethane, about 9.5% wt. of2-chloro-1,1,1,2-tetrafluoroethane and about 3.75% wt.4-isopropenyl-1-methyl cyclohexene, said fire extinguishing mixturebeing non-toxic and environmentally benign in both natural form anddegraded form on exposure to fire.
 3. A fire extinguishing mixtureconsisting of about 96% by weight of chlorodifluoromethane, and about 4%by weight of limonene, said fire extinguishing mixture being non-toxicand environmentally benign in both natural form and degraded form onexposure to fire.
 4. A fire extinguishing mixture consisting of about85% by weight of chlorodifluoromethane, about 11.5% by weight of1-chloro-1,2,2,2-tetrafluoroethane, and about 3.5% by weight ofdipentene, said fire extinguishing mixture being non-toxic andenvironmentally benign in both natural form and degraded form onexposure to fire.
 5. A fire extinguishing mixture consisting of about75% by weight of chlorodifluoromethane, about 11.75% by weight of1,1-dichloro-2,2,2-trifluoroethane, about 9.5% by weight of1-chloro-1,2,2,2-tetrafluoroethane, and about 3.75% by weight oflimonene, said fire extinguishing mixture being non-toxic andenvironmentally benign in both natural form and degraded form onexposure to fire.